The present invention relates to a crucible melting furnace, suitable in use for metal materials.
For example, crucible melting furnaces are used to cast products from non-iron metal materials such as aluminum. The crucible melting furnace generally has such a structure that a crucible is disposed inside a cylindrical furnace main body. A burner mounted below the crucible produces its flame toward the crucible.
In such a crucible melting furnace with the above construction, the flame from the burner is applied onto the bottom surface of the crucible at first. Next the flame climbs up along the side wall surfaces (outer circumference surfaces) of the crucible. However, the above-mentioned configuration has the following disadvantages.
(1) The flame applied to the bottom surface of the crucible rises up very quickly along the side wall surfaces of the crucible. Because of this construction, most of the heat energy is not utilized to fuse the metal material within the crucible. That is, the prior art furnace has a poor thermal efficiency.
(2) The flame is applied intensively to a specific portion of the crucible. For this reason, the temperature of a molten metal (a metal material in a liquid phase) within the crucible is considerably different from place to place. Such a phenomenon causes the quality of a product to be varied.
(3) As described in the item (2), the flame applied locally to a specific portion of the crucible tends to damage the specific portion. This results in shortening the life (serviceable life) of the crucible.
The present invention is made to solve the above-mentioned problems.
An object of the present invention is to provide a crucible melting furnace which has a high thermal efficiency and is capable of producing products with uniform quality and by which the temperature distribution of a molten metal within a crucible is small.
Moreover, another object of the present invention is to provide a crucible melting furnace which does not damage a crucible and can prolong the life (serviceable life) of the crucible.
In order to achieve the above-mentioned objects, according to the present invention, a crucible melting furnace comprises a crucible; and a thermal flow guide defined around the crucible, for guiding a thermal flow heating the crucible. The thermal flow guide has a guide for guiding the thermal flow along a spiral path defined around the crucible.
In the above-mentioned construction, the flame (thermal flow) produced by a burner are slowly carried away outside while being spirally rotated around the crucible along the outer circumference surfaces thereof. This structure largely increases the ratio of the heat energy used to fuse a metal material within the crucible, of the total heat energy of the flame (thermal flow). That is, the thermal efficiency is improved. Moreover, since the flame (thermal flow) does not intensively hit a specific portion of the crucible, it is hard that temperature differences occur in the molten metal within the crucible. This feature allows products with uniform quality to be obtained. Moreover, the above-mentioned structure does not substantially damage the crucible and can prolong the life (serviceable life) of the crucible.
The thermal flow guide can be comprised an outer circumference surface of the crucible and an annular fire-resistant wall disposed around the crucible. A spiral protruded streak formed on an inner circumference surface of the fire-resistant wall is utilized as the guide. As to the protruded streak, it is preferable that the width of the front end is shorter than that of the base end and that the cross section of the protruded streak has a trapezoid form. That is, by slanting the main surfaces (the upper surface and the lower surface) of the protruded streak, the thermal flow can be more effectively guided toward the crucible. As a result, the thermal efficiency can be improved.
Moreover, the ratio (a/b) of the height (a) of the protruded streak to the width (b) of the front end of the protruded streak is preferably 1.0 to 3.0, especially 1.5 to 2.5. That is, this range allows the thermal efficiency to be further improved and the life (serviceable life) of the crucible to be prolonged.
It is preferable that the fire-resistant wall comprises a composite material including a metal material and a ceramic material. With this structure, the protruded streak is difficult to be damaged due to heat and the life (serviceable life) of the crucible melting furnace is further prolonged.